The attacks come amid intense U.S. pressure on Pakistan to crack down on militants blamed for attacks both at home and on coalition forces in neighboring Afghanistan.

A truck bombing over the weekend at a luxury hotel in the capital Islamabad that killed 53 people underscored the threat extremists pose to the nuclear-armed nation.

More than 50 of the alleged insurgents, along with one soldier, died in clashes since Monday in Kohat region, which borders Pakistan's semiautonomous tribal areas, army spokesman Maj. Murad Khan said.

He said the military had retaken control of key mountain tunnel from the insurgents.

In the nearby Bajur tribal region, security forces killed at least 10 militants during an ongoing offensive there, government official Iqbal Khattak said.

That operation, which began in early August, has won praise from U.S. officials worried about rising violence in Pakistan and Afghanistan, but has triggered retaliatory suicide bombings elsewhere in Pakistan.

Some officials believe the weekend bombing of the Marriott Hotel may have been a response to the Bajur operations, which the army says has left more than 700 suspected militants dead.

'Mega-sanctuary'
Washington says the operation in Bajur — a rumored hiding place of al-Qaida leader Osama bin Laden — appears to have reduced violence across the border in Afghanistan.

Pakistan's army spokesman Maj. Gen. Athar Abbas has said Bajur had turned into a "mega-sanctuary" for militants and the military was determined to flush them out.

However, a rash of U.S. cross-border operations in neighboring tribal regions, including suspected missile strikes and a ground assault, underscore Washington's concerns that Pakistan is either unwilling or incapable of rooting out extremists on its own.

Pakistani President Asif Ali Zardari was expected to discuss the cross-border attacks with U.S. President George W. Bush on Tuesday on the sidelines of the U.N. General Assembly in New York.

In the latest such alleged breach, two U.S. helicopters crossed one mile into Pakistan late Sunday in the Alwara Mandi area in North Waziristan, two intelligence officials said on condition of anonymity because they were not authorized to speak to the media.

Citing informants in the field, they said Pakistani troops and tribesmen responded with small arms fire, but it was not clear whether the bullets were aimed at the choppers or were warning shots. The helicopters did not return fire and re-entered Afghan airspace without landing, the officials said.

'No such event'
That account was denied by Pentagon officials. "There was no such incursion, there was no such event," said Defense Department spokesman Col. Gary L. Keck.

Pakistan has protested U.S. cross-border operations, calling them violations of its sovereignty. But its government has called for diplomatic measures to resolve the dispute.

Zardari told NBC television in a recent interview that he welcomed U.S. intelligence help, but not its troops. "Give us the intelligence and we will do the job," he said. "It's better done by our forces than yours."

Experts and officials say the Marriott truck bombing bore the hallmarks of al-Qaida, but that the Taliban may still have assisted in its execution.

Late Monday, Dubai-based TV channel Al-Arabiya said it received a tape from a shadowy group calling itself "Fedayeen Al-Islam" — Arabic for "Islam commandos" — claiming responsibility for the Marriott bombing and calling on Pakistan to end cooperation with the United States.

The bombing at the hotel, a favorite spot for foreigners in Islamabad, has led diplomatic missions, aid groups and other expatriate organizations to review security measures.

A spokesman for British Airways on Tuesday said it was "indefinitely" suspending its flights to and from Pakistan "in light of the current security situation."

Meanwhile, the company that runs four visa application centers for the British High Commission in Pakistan has closed them pending a security review, commission spokesman Aidan Liddle said.

Copyright 2008 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.